Specialised placement of morphs within the gall of the social aphid <Emphasis Type="Italic">Pemphigus spyrothecae</Emphasis>

Background  

The strategic placement and aggregation of certain castes within the nests of eusocial insects such as bees and ants results in complex colonies that enjoy increased fitness through improved efficiency of social tasks. To examine if this advanced social phenomenon might apply to social aphids, the location of the numerous morphs within the nests (plant galls) of the aphid species Pemphigus spyrothecae was examined.     

Multiple endosymbionts in populations of the ant <Emphasis Type="Italic">Formica cinerea</Emphasis>

Background  

Many insects, including ants, are infected by maternally inherited Wolbachia endosymbiotic bacteria though other secondary endosymbionts have not been reported in ants. It has been suggested that the ability of Wolbachia to invade and remain in an ant population depends on the number of coexisting queens in a colony. We study the genetic and social structure of populations in the ant Formica cinerea which is known to have populations with either monogynous or polygynous colonies. We screen populations for several endosymbiotic bacteria to evaluate the presence of different endosymbionts, possible association between their prevalence and the social structure, and the association between endosymbiont prevalence and genetic differentiation of ant populations.     

Do host species evolve a specific response to slave-making ants?

Background

Social parasitism is an important selective pressure for social insect species. It is particularly the case for the hosts of dulotic (so called slave-making) ants, which pillage the brood of host colonies to increase the worker force of their own colony. Such raids can have an important impact on the fitness of the host nest. An arms race which can lead to geographic variation in host defenses is thus expected between hosts and parasites. In this study we tested whether the presence of a social parasite (the dulotic ant Myrmoxenus ravouxi) within an ant community correlated with a specific behavioral defense strategy of local host or non-host populations of Temnothorax ants. Social recognition often leads to more or less pronounced agonistic interactions between non-nestmates ants. Here, we monitored agonistic behaviors to assess whether ants discriminate social parasites from other ants. It is now well-known that ants essentially rely on cuticular hydrocarbons to discriminate nestmates from aliens. If host species have evolved a specific recognition mechanism for their parasite, we hypothesize that the differences in behavioral responses would not be fully explained simply by quantitative dissimilarity in cuticular hydrocarbon profiles, but should also involve a qualitative response due to the detection of particular compounds. We scaled the behavioral results according to the quantitative chemical distance between host and parasite colonies to test this hypothesis.

Results

Cuticular hydrocarbon profiles were distinct between species, but host species did not show a clearly higher aggression rate towards the parasite than toward non-parasite intruders, unless the degree of response was scaled by the chemical distance between intruders and recipient colonies. By doing so, we show that workers of the host and of a non-host species in the parasitized site displayed more agonistic behaviors (bites and ejections) towards parasite than toward non-parasite intruders.

Conclusions

We used two different analyses of our behavioral data (standardized with the chemical distance between colonies or not) to test our hypothesis. Standardized data show behavioral differences which could indicate qualitative and specific parasite recognition. We finally stress the importance of considering the whole set of potentially interacting species to understand the coevolution between social parasites and their hosts.

     

A molecular phylogeny of <Emphasis Type="Italic">Dorylus</Emphasis> army ants provides evidence for multiple evolutionary transitions in foraging niche

Background  

Army ants are the prime arthropod predators in tropical forests, with huge colonies and an evolutionary derived nomadic life style. Five of the six recognized subgenera of Old World Dorylus army ants forage in the soil, whereas some species of the sixth subgenus (Anomma) forage in the leaf-litter and some as conspicuous swarm raiders on the forest floor and in the lower vegetation (the infamous driver ants). Here we use a combination of nuclear and mitochondrial DNA sequences to reconstruct the phylogeny of the Dorylus s.l. army ants and to infer the evolutionary transitions in foraging niche and associated morphological adaptations.     

Intraspecific aggression and the colony structure of the invasive ant Myrmica rubra

1. Patterns of aggression between ants from different nests influence colony and population structure. Several species of invasive ants lack colony boundaries over large expanses, forming ‘supercolonies’ with many nests among which workers can move without encountering aggression. 2. Bioassays of aggression were used to determine the colony structure of the invasive ant Myrmica rubra (L.) at eight sites in Massachusetts, the state where the species was first discovered in North America. To improve the ability to distinguish systematic patterns from background variability in aggressiveness, a repeated‐measures design was used and replicate assays for each pair of nests were conducted. 3. Aggressive responses showed that populations at all sites consisted of multiple distinct colonies. Patterns of aggression were repeatable and transitive, with few exceptions. Colonies were identified as clusters of nests whose workers showed little to no aggression towards one another but were aggressive towards conspecifics from more distant nests. 4. The degree of aggression varied considerably among different colony pairs but did not depend in any consistent way on the distance of separation or on whether colonies were neighbours. 5. Territories of neighbouring colonies abutted, indicating that they were restricted by intraspecific competition. Mapped territories ranged in size from 0.03 to 1.2 ha, but colonies at the study sites have not undergone the enormous expansions seen in introduced populations of some other species of invasive ants, and neighbouring colonies compete locally.     

Genetic clusters and sex-biased gene flow in a unicolonial Formica ant

Background  

Animal societies are diverse, ranging from small family-based groups to extraordinarily large social networks in which many unrelated individuals interact. At the extreme of this continuum, some ant species form unicolonial populations in which workers and queens can move among multiple interconnected nests without eliciting aggression. Although unicoloniality has been mostly studied in invasive ants, it also occurs in some native non-invasive species. Unicoloniality is commonly associated with very high queen number, which may result in levels of relatedness among nestmates being so low as to raise the question of the maintenance of altruism by kin selection in such systems. However, the actual relatedness among cooperating individuals critically depends on effective dispersal and the ensuing pattern of genetic structuring. In order to better understand the evolution of unicoloniality in native non-invasive ants, we investigated the fine-scale population genetic structure and gene flow in three unicolonial populations of the wood ant F. paralugubris.     

Mechanisms of social regulation change across colony development in an ant

Background  

Mutual policing is an important mechanism for reducing conflict in cooperative groups. In societies of ants, bees, and wasps, mutual policing of worker reproduction can evolve when workers are more closely related to the queen's sons than to the sons of workers or when the costs of worker reproduction lower the inclusive fitness of workers. During colony growth, relatedness within the colony remains the same, but the costs of worker reproduction may change. The costs of worker reproduction are predicted to be greatest in incipient colonies. If the costs associated with worker reproduction outweigh the individual direct benefits to workers, policing mechanisms as found in larger colonies may be absent in incipient colonies.     

Genetic diversity and colony structure of Tapinoma melanocephalum on the islands and mainland of South China

Aim

Tapinoma melanocephalum is listed as one of the most important invasive pest species in China. Information regarding the patterns of invasion and effects of geographic isolation on the population genetics of this species is largely lacking.

Location

South China.

Methods

To address this problem, we genotyped 39 colonies (two colonies were collapsed due to genetic similarity) using microsatellite markers and mitochondrial DNA sequencing to compare colony genetic structure of T. melanocephalum on the mainland and islands of South China.

Results

An analysis of the colony genotypes showed that the genetic diversity of the mainland population was slightly higher than that of the island populations but not significantly so. However, the observed heterozygosity on Shangchuan Island (SCD) was significantly lower than that of the other colonies. We also found six haplotypes in 111 mitochondrial DNA COI sequences. The relatedness (r) value between colonies of SCD was 0.410, higher than that of the other populations. The genetic clusters among colonies were not related to geographic locations and exhibited admixture likely due to frequent human‐mediated dispersal associated with trade between the mainland population and the islands. Pairwise F_STs between populations showed differentiation among mainland populations, while SCD displayed high levels of divergence (F_ST > 0.15) from most mainland populations. There was no significant isolation by distance among colonies. Most populations showed signs of a bottleneck effect.

Main conclusions

Our study suggests that there was no significant difference in the genetic diversity among the islands and the mainland; however, the lower genetic diversity, the higher degree of genetic divergence from other colonies, and the higher relatedness among nestmates made the SCD population stand out from all the others.     

The diversity of microorganisms associated with <Emphasis Type="Italic">Acromyrmex</Emphasis> leafcutter ants

Background  

Molecular biological techniques are dramatically changing our view of microbial diversity in almost any environment that has so far been investigated. This study presents a systematic survey of the microbial diversity associated with a population of Acromyrmex leafcutter ants. In contrast to previous studies on social insects, which targeted specific groups of symbionts occurring in the gut (termites, Tetraponera ants) or in specialised cells (Camponotus ants) the objective of our present study was to do a total screening of all possible micro-organisms that can be found inside the bodies of these leafcutter ants.     

Blochmannia endosymbionts improve colony growth and immune defence in the ant Camponotus fellah

Background  

Microorganisms are a large and diverse form of life. Many of them live in association with large multicellular organisms, developing symbiotic relations with the host and some have even evolved to form obligate endosymbiosis [1]. All Carpenter ants (genus Camponotus) studied hitherto harbour primary endosymbiotic bacteria of the Blochmannia genus. The role of these bacteria in ant nutrition has been demonstrated [2] but the omnivorous diet of these ants lead us to hypothesize that the bacteria might provide additional advantages to their host. In this study, we establish links between Blochmannia, growth of starting new colonies and the host immune response.     

Asymmetric dispersal and colonization success of Amazonian plant-ants queens

Background

The dispersal ability of queens is central to understanding ant life-history evolution, and plays a fundamental role in ant population and community dynamics, the maintenance of genetic diversity, and the spread of invasive ants. In tropical ecosystems, species from over 40 genera of ants establish colonies in the stems, hollow thorns, or leaf pouches of specialized plants. However, little is known about the relative dispersal ability of queens competing for access to the same host plants.

Methodology/Principal Findings

We used empirical data and inverse modeling—a technique developed by plant ecologists to model seed dispersal—to quantify and compare the dispersal kernels of queens from three Amazonian ant species that compete for access to host-plants. We found that the modal colonization distance of queens varied 8-fold, with the generalist ant species (Crematogaster laevis) having a greater modal distance than two specialists (Pheidole minutula, Azteca sp.) that use the same host-plants. However, our results also suggest that queens of Azteca sp. have maximal distances that are four-sixteen times greater than those of its competitors.

Conclusions/Significance

We found large differences between ant species in both the modal and maximal distance ant queens disperse to find vacant seedlings used to found new colonies. These differences could result from interspecific differences in queen body size, and hence wing musculature, or because queens differ in their ability to identify potential host plants while in flight. Our results provide support for one of the necessary conditions underlying several of the hypothesized mechanisms promoting coexistence in tropical plant-ants. They also suggest that for some ant species limited dispersal capability could pose a significant barrier to the rescue of populations in isolated forest fragments. Finally, we demonstrate that inverse models parameterized with field data are an excellent means of quantifying the dispersal of ant queens.     

Parametric and non-parametric masking of randomness in sequence alignments can be improved and leads to better resolved trees

Background

Ants typically distinguish nestmates from non-nestmates based on the perception of colony-specific chemicals, particularly cuticular hydrocarbons present on the surface of the ants' exoskeleton. These recognition cues are believed to play an important role in the formation of vast so-called supercolonies that have been described for some invasive ant species, but general conclusions about the role of these cues are hampered by only few species being studied. Here we use data on cuticular hydrocarbons, aggression and microsatellite genetic markers to investigate the interdependence of chemical recognition cues, genetic distance and nestmate discrimination in the pharaoh ant (Monomorium pharaonis), a widespread pest species, and ask whether introduced populations of this species are genetically differentiated and exhibit intraspecific aggression.

Results

Microsatellite analyses of a total of 35 colonies from four continents revealed extremely high levels of genetic differentiation between almost all colonies (F _ST = 0.751 ± 0.006 SE) and very low within-colony diversity. This implies that at least 34 and likely hundreds more independent lineages of this ant have spread worldwide. Aggression tests involving workers from 14 different colonies showed only low levels of aggression, even between colonies that were geographically and/or genetically very distant. Chemical analyses of groups of worker ants showed that all colonies had the same cuticular compounds, which varied only quantitatively among colonies. There was a positive correlation between geographical and genetic distance, but no other significant relationships were detected between aggression, chemical profile, genetic distance and geographical distance.

Conclusions

The pharaoh ant has a global invasion history of numerous independent introductions resulting in genetically highly differentiated colonies typically displaying surprisingly low levels of intraspecific aggression, a behaviour that may have evolved in the native range or by lineage selection in the introduced range.     

Towards a molecular understanding of symbiont function: Identification of a fungal gene for the degradation of xylan in the fungus gardens of leaf-cutting ants

Background  

Leaf-cutting ants live in symbiosis with a fungus that they rear for food by providing it with live plant material. Until recently the fungus' main inferred function was to make otherwise inaccessible cell wall degradation products available to the ants, but new studies have shed doubt on this idea. To provide evidence for the cell wall degrading capacity of the attine ant symbiont, we designed PCR primers from conserved regions of known xylanase genes, to be used in PCR with genomic DNA from the symbiont as template. We also measured xylanase, cellulase and proteinase activities in the fungus gardens in order to investigate the dynamics of degradation activities.     

Under the volcano: phylogeography and evolution of the cave-dwelling Palmorchestia hypogaea (Amphipoda, Crustacea) at La Palma (Canary Islands)

Background

The invasive garden ant, Lasius neglectus, is the most recently detected pest ant and the first known invasive ant able to become established and thrive in the temperate regions of Eurasia. In this study, we aim to reconstruct the invasion history of this ant in Europe analysing 14 populations with three complementary approaches: genetic microsatellite analysis, chemical analysis of cuticular hydrocarbon profiles and behavioural observations of aggression behaviour. We evaluate the relative informative power of the three methodological approaches and estimate both the number of independent introduction events from a yet unknown native range somewhere in the Black Sea area, and the invasive potential of the existing introduced populations.

Results

Three clusters of genetically similar populations were detected, and all but one population had a similar chemical profile. Aggression between populations could be predicted from their genetic and chemical distance, and two major clusters of non-aggressive groups of populations were found. However, populations of L. neglectus did not separate into clear supercolonial associations, as is typical for other invasive ants.

Conclusion

The three methodological approaches gave consistent and complementary results. All joint evidence supports the inference that the 14 introduced populations of L. neglectus in Europe likely arose from only very few independent introductions from the native range, and that new infestations were typically started through introductions from other invasive populations. This indicates that existing introduced populations have a very high invasive potential when the ants are inadvertently spread by human transport.     

Colony social structure in native and invasive populations of the social wasp Vespula pensylvanica

Social insects rank among the most invasive of terrestrial species. The success of invasive social insects stems, in part, from the flexibility derived from their social behaviors. We used genetic markers to investigate if the social system of the invasive wasp, Vespula pensylvanica, differed in its introduced and native habitats in order to better understand variation in social phenotype in invasive social species. We found that (1) nestmate workers showed lower levels of relatedness in introduced populations than native populations, (2) introduced colonies contained workers produced by multiple queens whereas native colonies contained workers produced by only a single queen, (3) queen mate number did not differ significantly between introduced and native colonies, and (4) workers from introduced colonies were frequently produced by queens that originated from foreign nests. Thus, overall, native and introduced colonies differed substantially in social phenotype because introduced colonies more frequently contained workers produced by multiple, foreign queens. In addition, the similarity in levels of genetic variation in introduced and native habitats, as well as observed variation in colony social phenotype in native populations, suggest that colony structure in invasive populations may be partially associated with social plasticity. Overall, the differences in social structure observed in invasive V. pensylvanica parallel those in other, distantly related invasive social insects, suggesting that insect societies often develop similar social phenotypes upon introduction into new habitats.     

Gene expression and the evolution of phenotypic diversity in social wasps

Background  

Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution.     

Intraspecific Food‐Robbing and Neighborhood Competition: Consequences for Anti‐Robber Vigilance and Colony Productivity

Most social animals have mechanisms to distinguish group members from outsiders, in part to prevent the exploitation of resources reserved for members of the group. Nevertheless, specialized thieves of the Neotropical ant, Ectatomma ruidum, also known as the ‘thieving ant’, regularly enter and steal resources from distinct, neighboring colonies. Here, we examine the mechanisms and consequences of thievery in a population of E. ruidum. We show that (1) individuals from nearby colonies were accepted more often than those from farther colonies; (2) rejection rates decreased as individuals interacted more with non‐nestmates from the same source colony; and (3) colonies that were experimentally treated to reduce thievery rates had improved productivity. The boost in productivity with thievery reduction was greater in low density populations than in high density populations. We conclude that, as in other species, thievery has negative fitness costs to E. ruidum. However, greater acceptance of neighbors than non‐neighbors and increased acceptance after habituation to non‐nestmates suggest a proximate explanation for the presence of thievery. Moreover, lower fitness costs of thievery at high nesting density, combined with observations of extraordinarily high densities of E. ruidum throughout its range, suggest there is little selection pressure among these ants to guard against thieves, thus providing an ultimate explanation why thievery persists among litter‐foraging ants.     

Multiple virus infections occur in individual polygyne and monogyne Solenopsis invicta ants

Concurrent infections of Solenopsis invicta colonies with S. invicta virus 1 (SINV-1), SINV-2, and SINV-3 has been reported. However, whether individual ants were capable of supporting multiple virus infections simultaneously was not known, nor whether the social form of the colony (polygyne or monogyne) had an influence on the occurrence of multiple infection rates in individual ants. S. invicta field populations were sampled sequentially to establish whether multiple virus infections co-occurred in individual worker ants. In addition, the intra-colony virus infection rates were compared in monogyne and polygyne field colonies to determine whether social form played a role in the viral infection prevalence. All combinations of virus infection (SINV-1, SINV-2, or SINV-3 alone, SINV-1 & SINV-2, SINV-1 & SINV-3, SINV-2 & SINV-3, and SINV-1, SINV-2 & SINV-3) were detected in individual worker ants as well as queens in the field. Thus, individual S. invicta ants can be infected simultaneously with all combinations of the S. invicta viruses. Colony social form did have an influence on the intra-colony prevalence of multiple S. invicta virus infections. Polygyne colonies exhibited significantly greater intra- and inter-colony single and multiple virus infections compared with monogyne colonies.     

Effect of Invasive Species of Herbaceous Plants and Associated Aphids (Hemiptera,Sternorrhyncha: Aphididae) on the Structure of Ant Assemblages (Hymenoptera,Formicidae)

—In 2015–2017, attendance of 15 invasive and 22 native species of herbaceous plants by ants was studied in 6 habitats in the environs of Kyiv (Ukraine). Altogether, 14 ant species were found, of which 12 were recorded on invasive plants and 9 on native plants; 8 aphid species were found on 8 invasive plant species. Five invasive plant species (Asclepias syriaca, Heracleum mantegazzianum, Oenothera biennis, Onopordum acanthium, and Amaranthus retroflexus) were found to be attractive to ants, with over a half of all the ant workers in all the habitats being recorded on them; besides, numerous colonies of 7 aphid species were also found on these plants. These invasive plants positively affect the structure of ant assemblages since the aphid colonies provide ants with food resource. The remaining 10 invasive plant species, including 5 transformer species, were poorly visited by ants and housed no aphid colonies, with the exception of Conyza canadensis on which the non-myrmecophilous aphid Uroleucon erigeronense (Thomas, 1878) was found. Two thirds of invasive plant species had a negative effect on the structure of ant assemblages because they replaced the native plants and thus reduced the trophic resources of aphids.

     

蚂蚁入侵适应性进化及其机制

入侵种被传至一个新的区域后,在面对当地某些生态因子的胁迫时如何发生适应性变化,是入侵生物学研究的一个重要课题。这方面信息对评价物种的入侵性、制订防控策略具有重要指导意义。入侵性蚂蚁作为无脊椎陆生动物中入侵最成功、危害最严重的一类,其生物学、生态学已得到大量研究,许多报道表明它们在定殖和扩张过程中会发生适应性变化。基于30多年的文献资料,从蚁群社会结构、超级蚁群形成能力、个体大小、觅食行为、种间竞争、天敌防御、适应低温能力、生态位转变等多个角度进行了全面总结,并针对这些方面适应性变化的机制,从表型可塑性、适应性进化、自身遗传学基础、与共生微生物的互利关系等角度进行了剖析。提出了今后有待重点研究的几个问题。将有助于深化对蚂蚁成功入侵机制的认识,为推进我国红火蚁(Solenopsis invicta Buren)、小火蚁(Wasmannia auropunctata Roger)等入侵性蚂蚁的研究与治理提供参考。